Field of Invention
The invention relates to a method for selectively etching a structure pattern having a first and a second material layer on a substrate and specifically to reducing line edge roughness (LER) and achieve other target integration objectives in a directed self-assembly (DSA) process.
Description of Related Art
The need to remain competitive in cost and performance in the production of semiconductor devices has caused a continuous increase in device density of integrated circuits. To accomplish higher integration and miniaturization in a semiconductor integrated circuit, miniaturization of a circuit pattern formed on a semiconductor wafer must also be accomplished.
Photolithography is a standard technique used to manufacture semiconductor integrated circuitry by transferring geometric shapes and patterns on a mask to the surface of a semiconductor wafer. However, current state-of-the-art photolithography tools allow minimum feature sizes down to about 25 nm. Accordingly, new methods are needed to provide smaller features.
One type of structure pattern layer with a first and second material is a DSA layer. DSA layers include self-assembly of block copolymers (BCPs) which has been considered a potential tool for improving the resolution to better values than those obtainable by prior art lithography methods alone. Block copolymers are compounds useful in nanofabrication because they may undergo an order-disorder transition on cooling below a certain temperature (order-disorder transition temperature TOD) resulting in phase separation of copolymer blocks of different chemical nature to form ordered, chemically distinct domains with dimensions of tens of nanometers or even less than 10 nm. The size and shape of the domains may be controlled by manipulating the molecular weight and composition of the different block types of the copolymer. The interfaces between the domains may have widths of the order of 1 nm to 5 nm and may be manipulated by modification of the chemical compositions of the blocks of the copolymer.
A block copolymer may form many different phases upon self-assembly, dependent upon the volume fractions of the blocks, degree of polymerization within each block type (i.e., number of monomers of each respective type within each respective block), the optional use of a solvent and surface interactions. When applied in a thin film, the geometric confinement may pose additional boundary conditions that may limit the numbers of phases. In general, spherical (e.g., cubic), cylindrical (e.g., tetragonal or hexagonal) and lamellar phases (i.e., self-assembled phases with cubic, hexagonal or lamellar space-filling symmetry) are practically observed in thin films of self-assembled block copolymers, and the phase type observed may depend upon the relative volume fractions of the different polymer blocks. The self-assembled polymer phases may orient with symmetry axes parallel or perpendicular to the substrate and lamellar and cylindrical phases are interesting for lithography applications, as they may form line and spacer patterns and hole arrays, respectively, and may provide good contrast when one of the domain types is subsequently etched.
Two methods used to guide or direct self-assembly of a block copolymer onto a surface are grapho-epitaxy and chemical pre-patterning, also called chemi-epitaxy. In the grapho-epitaxy method, self-organization of a block copolymer is guided by topological pre-patterning of the substrate. A self-aligned block copolymer can form a parallel linear pattern with adjacent lines of the different polymer block domains in the trenches defined by the patterned substrate. For instance, if the block copolymer is a di-block copolymer with A and Bblocks within the polymer chain, where A is hydrophilic and B is hydrophobic in nature, the A blocks may assemble into domains formed adjacent to a side-wall of a trench if the side-wall is also hydrophilic in nature. Resolution may be improved over the resolution of the patterned substrate by the block copolymer pattern subdividing the spacing of a pre-pattern on the substrate.
In chemi-epitaxy, the self-assembly of block copolymer domains is guided by a chemical pattern (i.e., a chemical template) on the substrate. Chemical affinity between the chemical pattern and at least one of the types of copolymer blocks within the block copolymer chain may result in the precise placement (also referred to herein as “pinning”) of one of the domain types onto a corresponding region of the chemical pattern on the substrate. For instance, if the block copolymer is a di-block copolymer with A and B blocks, where A is hydrophilic and B is hydrophobic in nature, and the chemical pattern comprises of a surface having hydrophobic regions adjacent to regions that are neutral to both A and B, the B domain may preferentially assemble onto the hydrophobic region and consequently force subsequent alignment of both A and B blocks on the neutral areas. As with the grapho-epitaxy method of alignment, the resolution may be improved over the resolution of the patterned substrate by the block copolymer pattern subdividing the spacing of pre-patterned features on the substrate (so-called density or frequency multiplication). However, chemi-epitaxy is not limited to a linear pre-pattern; for instance, the pre-pattern may be in the form of a 2-D array of dots suitable as a pattern for use with a cylindrical phase-forming block copolymer. Grapho-epitaxy and chemi-epitaxy may be used, for instance, to guide the self-organization of lamellar or cylindrical phases, where the different domain types are arranged side-by-side on a surface of a substrate.
Accordingly, to achieve the advantages provided by grapho-epitaxy and chemi-epitaxy of block copolymers, new lithographic patterning and directed self-assembly techniques are required, including the ability to integrate such materials in patterning workflows. One example of a block copolymer is polystyrene-b-poly(methyl methacrylate) (PMMA). However, when removing the PMMA portion from the polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) layer to leave behind a polystyrene (PS) pattern, conventional etching techniques have suffered. Due to the organic nature of both materials, and their similarities, developing an etch chemistry with suitable etch selectivity has been challenging. Furthermore, conventional etch processes produce pattern defectivity, such as line edge roughness/line width roughness (LER/LWR), that are unacceptable as per the semiconductor device performance requirements. In extreme cases, the defectivity of the PS can be catastrophic due to pattern collapse as will be discussed in more detail below.
In future schemes, the ability to selectively remove one material while retaining the other material using dry etching techniques is paramount for the success for such patterning implementation. As mentioned above, acceptable critical dimension (CD), LER/LWER and etch selectivity are major factors that determine usefulness of an integration process that is used for self-aligned quadruple patterning (SAQP) process. The current methods do not provide the CD, LER, and LWR that are required as the need for higher density patterns increases. There is also a need to ascertain the combination of flowrates or ratios of etchant gases or combination of gases that provide the etch sensitivity required. Overall, there is a need for controlled etching techniques, processes, combination of etchant gases that produce acceptable etch selectivity, and LER results in order to achieve integration objectives with smaller features.